(300e) Pervaporation-Assisted Furfural Production from Xylose
Furfural produced from the biomass-derived xylose may serve as a platform molecule for the sustainable production of fuels, lubricants, and other specialty chemicals. The acid-catalyzed dehydration of xylose to furfural is burdened by side reactions that form degradation products, known as humins, which reduce the yield of furfural. The formation of humins can be minimized by removal of furfural during its production. In aqueous-phase reactions, this is conventionally achieved by steam stripping, but may also be accomplished by pervaporation, a membrane process. The goal of this study was to demonstrate improvements in pervaporation-assisted furfural production. We previously described a pervaporation-assisted reactor which improved furfural production compared to a membrane-free reactor, but it was limited by two main factors: (1) permeation-induced depletion of reaction-volume which restricted experiments to moderate xylose conversion, and (2) interstage cooling and heating required to accommodate the relatively low membrane temperature. We improved upon the system by incorporating an inlet flow to balance the permeation of material from the reactor. This permitted the study of complete-conversion batch reactions and continuous pervaporation-assisted furfural production. Furthermore, we used cross-linked polymer membranes, which allowed us to eliminate the interstage cooling and heating and to operate the pervaporation-assisted reactor isothermally. This resulted in improved membrane performance as a consequence of increased flux. We then explored the use of metal halides as homogeneous catalysts for pervaporation-assisted reactions, which have combined Lewis- and Brønsted-acid functionality and have been shown previously to produce furfural selectively. While homogeneous catalysts are traditionally thought to be cumbersome because of the need for product/catalyst separation, we show that such a separation is simplified in a pervaporation-assisted reactor because of the lack of permeation of the metal halide catalysts.